package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.io.Closeable;

/** Abstract base class for input from a file in a {@link Directory}.  A
 * random-access input stream.  Used for all Lucene index input operations.
 * @see Directory
 */
public abstract class IndexInput extends DataInput implements Cloneable, Closeable {

    /**
     * Expert
     * 
     * Similar to {@link #readChars(char[], int, int)} but does not do any conversion operations on the bytes it is reading in.  It still
     * has to invoke {@link #readByte()} just as {@link #readChars(char[], int, int)} does, but it does not need a buffer to store anything
     * and it does not have to do any of the bitwise operations, since we don't actually care what is in the byte except to determine
     * how many more bytes to read
     * @param length The number of chars to read
     * @deprecated this method operates on old "modified utf8" encoded
     *             strings
     */
    @Deprecated
    public void skipChars(int length) throws IOException {
        for (int i = 0; i < length; i++) {
            byte b = readByte();
            if ((b & 0x80) == 0) {
                //do nothing, we only need one byte
            } else if ((b & 0xE0) != 0xE0) {
                readByte();//read an additional byte
            } else {
                //read two additional bytes.
                readByte();
                readByte();
            }
        }
    }

    private final String resourceDescription;

    /** @deprecated please pass resourceDescription */
    @Deprecated
    protected IndexInput() {
        this("anonymous IndexInput");
    }

    /** resourceDescription should be a non-null, opaque string
     *  describing this resource; it's returned from
     *  {@link #toString}. */
    protected IndexInput(String resourceDescription) {
        if (resourceDescription == null) {
            throw new IllegalArgumentException("resourceDescription must not be null");
        }
        this.resourceDescription = resourceDescription;
    }

    /** Closes the stream to further operations. */
    public abstract void close() throws IOException;

    /** Returns the current position in this file, where the next read will
     * occur.
     * @see #seek(long)
     */
    public abstract long getFilePointer();

    /** Sets current position in this file, where the next read will occur.
     * @see #getFilePointer()
     */
    public abstract void seek(long pos) throws IOException;

    /** The number of bytes in the file. */
    public abstract long length();

    /**
     * Copies <code>numBytes</code> bytes to the given {@link IndexOutput}.
     * <p>
     * <b>NOTE:</b> this method uses an intermediate buffer to copy the bytes.
     * Consider overriding it in your implementation, if you can make a better,
     * optimized copy.
     * <p>
     * <b>NOTE</b> ensure that there are enough bytes in the input to copy to
     * output. Otherwise, different exceptions may be thrown, depending on the
     * implementation.
     */
    public void copyBytes(IndexOutput out, long numBytes) throws IOException {
        assert numBytes >= 0 : "numBytes=" + numBytes;

        byte copyBuf[] = new byte[BufferedIndexInput.BUFFER_SIZE];

        while (numBytes > 0) {
            final int toCopy = (int) (numBytes > copyBuf.length ? copyBuf.length : numBytes);
            readBytes(copyBuf, 0, toCopy);
            out.writeBytes(copyBuf, 0, toCopy);
            numBytes -= toCopy;
        }
    }

    @Override
    public String toString() {
        return resourceDescription;
    }
}
